Ideal for lines with rapid changes in pressure and flow, these couplings have threads that lock them together. They connect more securely than push-to-connect couplings, whose bearings wear out in high-impulse conditions. A complete coupling consists of a plug and socket (both sold separately). To limit fluid loss when you connect and disconnect them, they both have flat faces for a close fit, as well as shut-off valves to stop flow. For these reasons, they’re also known as flush-face and double shut-off couplings. They meet ISO 18869, which is an international standard that defines methods for testing and evaluating the performance of screw-to-connect hydraulic couplings.

To make a coupling, align the plug and socket, then push and turn the socket sleeve toward the plug while engaging the threads. Allow the threads to pull the sleeve onto the plug; do not push the sleeve onto the plug. Thread until the sleeve meets the plug body—start by hand, and if pressure built up inside the hose makes the two halves hard to connect, use a wrench to finish the job. To disconnect, unlock the socket sleeve with a wrench, then unthread by hand while keeping the halves aligned. Stop the flow before you disconnect the line.

Note: To ensure a correct fit, make sure that the plug and socket have the same coupling size. Pressure ratings are given for static (constant) pressure conditions.